linux-kernel - Re: [PATCH v3 5/7] bdev: add open

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Date:   Thu, 21 Nov 2019 11:06:14 +0100
From:   Michal Suchánek <msuchanek@...e.de>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     linux-scsi@...r.kernel.org, Matthew Wilcox <willy@...radead.org>,
        "Ewan D. Milne" <emilne@...hat.com>,
        Jonathan Corbet <corbet@....net>, Jens Axboe <axboe@...nel.dk>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "J. Bruce Fields" <bfields@...hat.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Eric Biggers <ebiggers@...gle.com>,
        Benjamin Coddington <bcodding@...hat.com>,
        Hannes Reinecke <hare@...e.com>,
        Omar Sandoval <osandov@...com>, Ming Lei <ming.lei@...hat.com>,
        Damien Le Moal <damien.lemoal@....com>,
        Bart Van Assche <bvanassche@....org>,
        Tejun Heo <tj@...nel.org>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v3 5/7] bdev: add open_finish.

On Mon, Nov 04, 2019 at 04:17:27PM -0800, Christoph Hellwig wrote:
> Please make sure you CC linux-block if you add block device ops.
> 
> On Fri, Oct 25, 2019 at 01:21:42PM +0200, Michal Suchanek wrote:
> > Opening a block device may require a long operation such as waiting for
> > the cdrom tray to close. Performing this operation with locks held locks
> > out other attempts to open the device. These processes waiting to open
> > the device are not killable.
> > 
> > To avoid this issue and still be able to perform time-consuming checks
> > at open() time the block device driver can provide open_finish(). If it
> > does opening the device proceeds even when an error is returned from
> > open(), bd_mutex is released and open_finish() is called. If
> > open_finish() succeeds the device is now open, if it fails release() is
> > called.
> > 
> > When -ERESTARTSYS is returned from open() blkdev_get may loop without
> > calling open_finish(). On -ERESTARTSYS open_finish() is not called.
> > 
> > Move a ret = 0 assignment up in the if/else branching to avoid returning
> > -ENXIO. Previously the return value was ignored on the unhandled branch.
> 
> Still a complete nack for splitting a fundamental operation over two
> ops, especially just for working around a piece of buggy software.

Still did not provide an awesome alternative that does not sneed
splitting the operation.

What is it, specifically?

Thanks

Michal